July 28, 2010  -- The indictment of a UPS worker has stunned the Maryland community where two mother-daughter pairs were murdered in a two-month period.

"To do this without knowing a person, that you could be so evil, not knowing a person and you want to do this, that is so sad to be so evil," said Rosa Smith, mother of Delores DeWitt, who was killed in March.

Jason Thomas Scott, 27, was charged Tuesday in the murder of Delores and Ebony Dewitt, a mother and daughter who were found in a burning car in March 2009. A Prince Georges grand jury returned a seven-count indictment against Scott, including two counts of murder and two counts of burglary.

Law enforcement sources said they believe Scott also killed Karen and Karissa Lofton two months prior in their locked home.

Authorities believe Scott had been leading a double life, working at UPS by day, but also allegedly using his computer skills to research police forensic tactics and possibly using his UPS database to research alleged victims.

UPS officials said they have yet to be questioned.

Maryland Community Shaken

The horror began Jan. 26, 2009, in Prince Georges County, Maryland, as an intruder neutralized the Loftons' home alarm system and slipped inside.

Karen Lofton, a 45-year-old nurse, was fatally shot as she tried to hide in a corner. Her daughter Karissa, 16, was repeatedly shot as she frantically dialed 911 from her bed.

Police were perplexed. The doors were locked and there were no signs of forced entry. Neighbors were terrified.

"Until they catch him, I will be afraid," said one woman.

On March 16, the bodies of Delores Dewitt, a 42-year-old nurse, and her 20-year-old daughter, Ebony, were found in a burning car less than a mile away from the Loftons' home. The car had been stolen that day.

The Dewitts lived within a mile of the Loftons.

"She [Delores] was a beautiful person, had a beautiful spirit and was just a wonderful person all around. And so was Ebony," said a friend at a memorial service for the Dewitts.

"My heart is aching. I am hurting because I lost a friend," said another grieving attendee.

Similarities and Stark Differences

Authorities wondered whether this was the work of a serial killer. There were similarities -- two mother-daughter pairs; two nurses in their 40s -- but also stark differences. The Loftons were shot in their home in what appeared to be a controlled, planned execution. The Dewitts might have been killed in a random act of violence, perhaps a carjacking. It was unknown whether they had also been shot.

Five Murders in Nine Months

"We don't have any evidence this is a serial killer but the coincidences between these cases are very strong," said a police officer after the Dewitts' bodies were found.

An FBI profiler thought that the killer had acted differently in each case and that the cases were probably not linked. Still the residents of Prince Georges County knew something horrible was happening.

"I have daughters who are driving now and I'm afraid for them," said one neighbor. "I tell them to lock their doors when they get in the cars. I don't want them walking alone at nighttime."

Authorities suspect that Scott also killed Vilma Artis Butler, who was found dead in her burning home in Bowie, Md., in June 2008. Some police worry that Scott might be responsible for other unsolved deaths in Washington, D.C., Texas and Florida, where he is also known to have frequented.

He has a degree in computer science at the University of Maryland and had worked at UPS. According to law enforcement sources, Scott may have used the company's database to help select victims. He lived close to the Dewitts in Upper Marlboro, Md.

Susan C. Aldridge, president of the University of Maryland University College, released this statement: "We were disturbed and deeply saddened to learn that evidence links these horrible crimes to a graduate of this institution. .... Our deepest sympathies go out to the families and friends of the victims."

Sources tell ABC News that police found material on Scott's computer that revealed he was researching police investigative tactics and forensic capabilities.

Police suspect that Scott used bleach to clean his crime scenes and arson to destroy evidence. They also suspect that he altered the placement of the bodies to confuse people.

He was arrested in July 2009 in a UPS parking lot after the Bureau of Alcohol, Tobacco, Firearms and Explosives got a tip that he was selling weapons out of the trunk of his vehicle. He was charged with selling 14 stolen guns including pistols, assault weapons, silencers and a machine gun. He remains jailed on weapons and carjacking charges.

The investigation eventually led authorities to an old mansion that police believe served as a thieves' lair. It was there, sources say, that investigators found evidence linking him to the crime scenes of the murders of the Loftons and Dewitts.

Jason Thomas Scott: 'A Bad History'

"It all started around when he was 10 years old. Peeping Tom, recording people when they were sleep or undressing," said an Upper Marlboro neighbor. "Then it went from breaking and entering, stealing vehicles. Somehow being very, very intelligent led him to a very bad history."

Scott has a long criminal record, including charges of armed robbery and multiple charges of burglary. Scott is being held in the Prince George's detention center and will be arraigned in a few days.

If he is a serial killer, the new question facing investigators is whether they caught him at the start of his reign of terror or whether there many more victims to be found.