(CNN) The 27-year-old son of a Connecticut couple missing since early August has been charged with murder in the death of his parents.

Kyle Navin was charged Friday with two counts of murder and two counts of murder with special circumstances in the disappearance of his parents, Jeffrey and Jeanette Navin, Connecticut State Police said.

His girlfriend, Jennifer Valiante of Westport, Connecticut, is also facing charges of conspiracy to commit murder and hindering prosecution.

Navin is being held on a $2.5 million bond, Valiante on a $2 million bond.

Navin's attorney, Eugene Riccio, has not returned calls seeking comment on his client's case.

Valiante's attorney, Elliot Warren, declined comment.

Kyle Navin's parents were last seen August 4, days after losing an appeal in a multimillion-dollar foreclosure case at the trash removal and recycling company they owned in Easton, Connecticut.

Human remains found Friday in a vacant lot less than 10 miles away were positively identified as the missing couple, the Office of the Chief Medical Examiner said.

A lengthy affidavit in support of Valiante's arrest warrant describes Kyle Navin's long-troubled relationship with his parents.

A tumultuous relationship

The parents had expressed to friends concern about their son's alleged heroin use, according to the affidavit. The couple planned to sell their trash removal company and cut their son out of their will, leaving him on his own financially, said the affidavit from a state police major crime investigator.

A friend of Jeanette Navin told investigators that the couple had bought their son a house in his name but he failed to pay the mortgage or taxes, the affidavit said. The home was purchased in cash and Kyle Navin owed his parents $133,000, according to the court document.

On May 14, Kyle Navin told Valiante in a text message that they needed to figure out the best way to "take them down," referring to his parents, and "get some money out of them somehow," according to the affidavit.

In other text messages to Valiente, Kyle Navin referred to a plan to "solve every single problem and give us a wealthy amazing life" and "wipe out the infection and get $ for life."

Investigators learned that the tumultuous relationship between the couple and their son included Jeffrey Navin's "history of being emotionally and verbally abusive towards his son Kyle," the court document said. The alleged abuse was investigated by state child welfare authorities, the affidavit said.

Gun charge hearing

Kyle Navin appeared Friday at a detention hearing on an unrelated gun charge. A judge ordered then that Navin be kept in custody.

He had been arrested and charged September 8 with "possession of a firearm by an individual who is an unlawful user of or addicted to any controlled substance," according to federal court records.

Four days after the couple were last seen, police found a blue pickup belonging to them in a commuter parking lot off an exit on Merritt Parkway, according to Easton Police Chief Tim Shaw.

William Navin, Jeffrey's brother and co-owner of the refuse company, told Easton police that his brother had not shown up for work, which was highly unusual, an affidavit said. He also said that Kyle Navin was the last to see the couple.

Family members and friends had been trying to call the Navins, but their phones appeared to have been turned off, according to Jeffrey Navin's brother.

Law enforcement officers later obtained cell data for the couple. Both phones pinged the same cell tower in Bridgeport, Connecticut -- "in the vicinity of (Kyle) Navin's residence," the affidavit said.

Police: inconsistent accounts

The same day the Navins were reported missing, law enforcement officers spoke to Kyle Navin.

He confirmed to police that he saw his parents the morning of August 4 and that they invited him to dinner that evening, but he declined because he was in pain from a back injury, the affidavit said.

Authorities interviewed Kyle Navin three more times during a 10-day period. He gave police inconsistent accounts of the interactions he had with his parents the last time that they were seen, the affidavit said.

Kyle Navin said he picked up his mother at a parking lot off the Merritt Parkway in his garbage truck, and the two went to collect refuse along his usual route, according to the affidavit. Around 9 a.m., Kyle's back began to bother him, and the two eventually met up with his father so his son could go home.

Authorities determined that his varying accounts did not line up with cell phone data, which shows a different travel route for him, according to the affidavit.

Cell phone records

Kyle Navin also told authorities he continued to contact his father via telephone the afternoon of August 4 solely about work and his back injury.

But cell phone records reviewed by law enforcement officers show otherwise:

"I'm not going home till I know mom is okay... did you hurt mom?" said a text message Jeffrey Navin sent to his son, according to the affidavit.

"No Absolutely not. Why would you think," Kyle replied.

"I go home and get framed for murder... I'm going to the police first," the father responded.

A half hour before Jeffrey Navin's phone is last registered as being used -- at 12:57 p.m. -- there was another text message to his son: "U R setting me up."

Two hours later, a security camera video also captured Jeffrey Navin's garbage truck being driven toward the couple's home with the car of Kyle's girlfriend following behind, the affidavit said.

Nearly 30 minutes later, the girlfriend's car was spotted going in the opposite direction. The girlfriend later told authorities that Kyle drove his father's truck to their home, she followed him and then drove him back to their residence and "could offer no reason as to why or how Jeffrey's truck came to be in Bridgeport or why Navin needed to drive the truck back to Easton."

Firearms seized

During a search of Kyle Navin's residence, officers seized two firearms and rounds of ammunition as well as hypodermic needles, glassine bags with "what appeared to be heroin residue," empty prescription bottles for Oxycodone and prescription bottles with controlled substances such as Xanax, the affidavit said.

Also recovered from the home was a receipt from Home Depot issued on August 5 showing Kyle Navin purchased "germicidal bleach, hair/grease drain opener, 'Goo Gone' stain remover and contractor cleanup bags," the affidavit said.

Navin previously told authorities he learned about the "mystery" of his parents' whereabouts when his uncle called him on August 6, according to the affidavit.