Terror investigators have found a suspicious $28,000 deposit was made into the bank account of the San Bernardino gunman, just two weeks before he and his wife gunned down 14 and injured 21.

The latest finding raises the chilling possibility that Syed Rizwan Farook and his wife Tashfeen Malik had outside help in their attack on the Inland Regional Center.

It comes as the FBI revealed the terror couple had been radicalized for 'some time' since they settled into married life in America in July 2014.

It has also emerged that they were targeting first responders with the pipe bombs they planted in the center and hoped to kill the brave men and women who rushed to the scene of the shootings.

Thankfully the bombs failed to detonate either due to a remote control malfunction or as a result of the buildings overhead emergency sprinklers.

This image shows San Bernardino shooters Tashfeen Malik and Syed Farook going through customs as O'Hare Airport in Chicago in July 2014 upon their arrival from Saudi Arabia

A bag stuffed with homemade pipe bombs was recovered from Malik and Farook's home after Wednesday's attack at the Inland Regional Center in San Bernardino, California, on Wednesday

'This was meant to kill more, but also scare other future responders to attacks,’ a source with inside knowledge of the investigation told Fox News of the bombs. ‘This was meant to get into the minds of medics and officers who are arriving first on scene.’

News of the bombs was revealed after David Bowdich, assistant director of the FBI's Los Angeles office, announced on Monday that Farook and Malik were radicalized and had been 'for some time'. He added the bureau doesn't know when or how they were radicalized.

It was also revealed on Monday that a $28,000 deposit was made into Farook’s bank account on or around November 18 from WebBank.com.

Investigators are now looking into whether the transaction was a loan. Farook earned $53,000 a year as an environmental health inspector for San Bernardino County.

WebBank.com, a Utah-based company, describes itself on its website as ‘ a leading provider of national consumer and commercial private-label and bank card financing programs’ on a nationwide basis.

Farook converted $10,000 of the $28,000 to cash on or about November 20, and withdrew the money from a Union Bank in San Bernardino.

In the days leading up to the massacre, at least three transfers of $5,000 appeared to go to Farook’s mother.

An AR-15 assault rifle at Riverside Magnum Shooting Range earlier this year. Farook is said to have visited the range 'with frequency'

Investigators said that both Farook, (left) and his wife Tashfeen Malik (right) practiced 'dry-firing' without bullets in a backyard

Range owner Peter Lee (pictured) said that Farook probably visited the establishment frequently

Farook reportedly spent hours at the shooting range (pictured) during one session, and used both a AR-15 assault rifle and a handgun

The loan and cash withdrawal were described as ‘significant evidence of pre-meditation’, a source told Fox News, which further undercuts the possibility of the shooting stemming from a disagreement at a work Christmas party.

Investigators are also reportedly looking into whether the $10,000 cash withdrawal was used to reimburse Enrique Marquez Jr, a security guard friend of Farook’s who is the man who bought the two semi-automatic rifles used in the attack.

The shooters themselves are thought to have bought handguns that were also used.

Marquez checked himself into a mental hospital after the killings, and FBI agents raided his home on Sunday. He is now reportedly answering investigators’ questions.

‘Right now our major concern at the FBI, the ATF, and the JTTF (Joint Terrorism Task Force) is determining how those firearms, the rifles in particular, got from Marquez to Farook and to Malik,’ assistant special agent in charge with the Bureau of Alcohol, Tobacco and Firearms, John D’Angelo, said on Monday.

The weapons were all purchased legally in California between 2007 and 2012.

FBI agents are also looking into evidence of pre-meditation with an SUV rental charge that was processing on Farook’s account on November 30, two days before the shooting.

It has been revealed that the gunmen practiced shooting at a local firing range before Wednesday’s massacre, investigators said.

Farook, 28, went to Riverside Magnum Shooting Range, 25 miles from his home in Redlands, California, twice in the days before carrying out the terrorist attack with his wife Malik.

David Bowdich (center), assistant director of the FBI's Los Angeles office, said the bureau now believes both Farook and Malik were radicalized and had been 'for some time'

The couple were armed with a .223-caliber DPMS Model A15 rifle, a Smith and Wesson M&P15 rifle as well as Llama handgun and a Smith and Wesson handgun (pictured)

Thousands of rounds of ammunition were discovered in the attackers' apartment, as well as in the car where they died in a shootout with police

Farook made visits to the Riverside range and fired both and AR-15 assault rifle and a handgun on the Sunday and Monday before the massacre, spending several hours there during one session.

His wife joined him on at least one of those occasions, Bowdich said on Monday.

TIMELINE OF TERROR MARRIAGE Tashfeen Malik entered the US for the first time on July 27, 2014, on a K-1 or 'fiance' visa. The visa program allows foreign residents intending to marry American citizens to live with them in the US for up to 90 days prior to the wedding. Before entering the country, the partner has to undergo several rounds of counter-terrorism screening and a medical exam. Malik would have also had to undergo a one-on-one interview with an embassy official in her home country of Pakistan. However, already questions are swirling about how the checklist works. For example, Fox News reported that Malik cited an incorrect home address in Pakistan on her visa application and it wasn't picked up by the authorities. The couple reportedly met on a Muslim dating website sometime in 2013. They came face-to-face for the first time in Saudi Arabia in July 2014 when Farook took a two-week vacation to meet his bride-to-be and her family. A new photograph shows the new couple arriving in Chicago's O'Hare International Airport on the evening of July 27, 2014. The pair were reportedly married in Riverside, California, in August 2014. Farook petitioned to have his wife's immigration status changed to Legal Permanent Resident in September. It is likely the couple also had a religious ceremony in Saudi Arabia before Malik moved to the US, although this hasn't been confirmed. Advertisement

Bowdich said in an afternoon press conference on Monday that both Malik and Farook had been to ranges before the attack.

Investigators also told Fox News that the couple were ‘dry-firing’ in another Southern California home's backyard before the attack, meaning that they were practicing pulling the trigger but had no bullets in the chamber.

‘The intent is to train the mind to kill,’ a source told Fox of the preparations.

The shooting range’s owner Peter Lee said that he had been on a cruise in the lead-up to the shootings, but that the FBI contacted him on Wednesday night and later took his video surveillance and financial statements.

He told Hoy Los Angeles that Farook probably visited his shooting range ‘with frequency’.

Riverside Magnum offers unlimited time in a shooting lane for $15, and has guidelines including no rapid firing inside the range.

It also offers gun rentals, though Farook brought his own guns with him.

Modified AR-15s were the guns used by the attacker and his wife during the massacre at Inland Regional Center

Increased scrutiny has focused on how Farook and Malik acquired their guns, ammo and stockpile of homemade pipe bombs.

Receipts for two online gun stores, Budsgunshop.com and Cheaper than Dirt, were found in their home.

More than 4,500 rounds of ammunition and a dozen pipe bombs were found in Farook and Malik’s home, leading some to believe they planned on more attacks.

Investigators also found 19 pipes in the couple's home that could be turned into bombs with all the right components.

An additional 1,600 rounds of ammunition were found in the rental car where the couple were killed.

In the wake of the attack, Syed Farook's 66-year-old father, also named Syed Farook, has been placed on a federal watch list.

Pictures of the victims of Wednesday's mass shooting are displayed during a candlelight vigil in downtown San Bernardino on Monday

People hold candles during a vigil for the 14 victims who were shot dead by Farook and Malik in San Bernardino

People gather around a makeshift memorial outside the Inland Regional Center during a vigil on Monday

People light one another's candels during a vigil held on Monday night in San Bernardino following last week's shooting

An official familiar with the FBI investigation told ABC News that the elder Mr Farook has made multiple lengthy trips to Pakistan, including this and last year.

In an interview with an Italian newspaper over the weekend, the elder Syed Farook reportedly said that his son was fascinated with ISIS and hated the State of Israel.

Other family members have since downplayed Ms Farook's remarks, saying he is 'not stable ' and 'not handling this well’. The father himself later said he did not recall talking to the newspaper.

The FBI is also investigating exactly how much Farook’s mother knew about the impending attack.

Rafia Sultana Farook, 62, lived in the same home in Redlands, California, as her son and his wife built a dozen pipe bombs and stored 6,000 rounds of ammunition.

In a press conference on Friday, attorneys David Chesley and Mohammed Abuershaid, who represent the Farook family, said that Rafia had been extensively questioned by the FBI following the shooting and there was no evidence she had prior knowledge of the attack.

An image emerged on Monday showing Farook and Malik as newlyweds entering the United States upon their arrival from Saudi Arabia last year - as the FBI revealed that both shooters were radicalized.

The image, first obtained by ABC News Monday morning, was apparently taken as Syed Farook and his bride, Tashfeen Malik, were going through customs in Chicago's O'Hare International Airport on the evening of July 27, 2014. It marks the first time that the couple are seen posing together.

The photograph depicts Malik, 29, dressed in a black hijab on her head and what appears to be a matching dress, staring stone-faced straight into the camera in her first moments on US soil.

Malik is seen here in a photo ID from Bahauddin Zakaria University in Multan, Pakistan, where she had studied pharmacy

The Pakistan identification card of Tashfeen Malik, who came to the US from Saudi Arabia on a K-1 visa

Farook, 28, wearing a loose light-colored shirt and a skull cap, stands a few paces behind his partner.

The future San Bernardino gunman is sporting a beard but no mustache in the photo. The couple are wearing blank expressions in the photo.

The release of the first known photo of the terrorist duo comes as federal officials continue to delve into Malik and Farook's biographies in an effort to trace their path to radicalization, and learn what contacts the woman might have had with Islamic militants in Pakistan and Saudi Arabia, where she grew up.

The FBI is investigating how much Farook’s mother, Rafia Sultana Farook (left), 62, knew about the impending attack. Rafia lived in the same home in Redlands, California, as her son and his wife

Malik's estranged relatives in Pakistan have said she appeared to have abandoned the family's moderate Islam and become more radicalized in Saudi Arabia, where she moved as a toddler.

She returned to Pakistan and studied pharmacy at Bahauddin Zakaria University in Multan from 2007 to 2012.

While in Multan, she also attended a religious school, which Pakistani intelligence officials on Monday identified it as the Al-Huda International Seminary. The school is a women-only madrassa with a chain across Pakistan and branches in the U.S. and Canada, said the officials, speaking on condition of anonymity in line with regulations.

Malik spent more than a year at Al-Huda, taking classes six days a week, the school's spokeswoman Farrukh Chaudhry told The Associated Press.

She enrolled in a two-year course to learn the Muslim holy book, Quran, its translation and interpretation but did not finish the course, Chaudhry added. Malik was a student there from April 17, 2013 until May 3, 2014, when she handed in her last paper in the first-year curriculum, the spokeswoman said.

US Attorney General Loretta Lynch said US authorities have no evidence that the shooters were part of a larger terrorism cell but were working with their counterparts overseas to gather information about their lives.

'We are trying to learn everything we can about both of these individuals,' Lynch said on NBC's Meet the Press. 'It will be a long process, it will be an exhaustive process.

Under scrutiny: Farook's 66-year-old father, a naturalized US citizen also named Syed Farook (pictured December 7 in Riverside), has been placed on a terror watch list

Accused: Enrique Marquez, 29, allegedly purchased assault-style weapons for the San Bernardino shooters

'And we are trying to learn as much as we can about her life before they met, after they met and frankly, after she came here as well. What we are trying to focus on again is what motivated these two individuals.'

Officials have acknowledged they had no information about the couple before the killing other than routine matters related to Malik's immigration status in the United States.

Malik and Farook reportedly met on a Muslim dating website sometime in 2013.

Investigators with the FBI previously revealed that Malik entered the US on a K-1 fiancee visa and married Farook in California a month later. The wedding in Riverside may have been preceded by an earlier religious ceremony in Saudi Arabia, according to some officials.

In late May of this year, the newlyweds welcomed their baby daughter, who is now 6 months old and an orphan after Malik and Farook were killed in a gun battle with police just hours after the Wednesday morning shooting rampage.

Newly released dispatch tapes showed police had the name of one of the California shooting suspects as officers swarmed the scene of the massacre.

Recordings posted by The Press-Enterprise newspaper include an officer saying Syed Farook was a possible suspect. The officer says Farook seemed nervous when he left the building in San Bernardino before the attack and he matched the description of a shooter.

Also on Monday, ABC News released what is believed to be the first recording featuring the 28-year-old gunman's voice.

Farook, who was born in Illinois to Pakistani parents, is heard stating his full name, 'Syed Farook,' in a clear voice, without any audible accent, in a voicemail greeting.

People pay respects at a makeshift memorial in San Bernardino honoring the victims of Wednesday's attack

Police respond to the scene of an active shooting at Inland Regional Center in San Bernardino on Wednesday