Investigators have uncovered at least seven bodies from the impassible swamp behind a New Britain shopping center and believe the victims died at the hands of a single person.

Multiple sources have told NBC Connecticut that person is 45-year-old William Devin Howell.

Howell is serving a 15-year sentence for manslaughter in connection with the death of Wethersfield resident Nilsa Arizmendi, who was last seen getting into Howell’s Ford Econoline van in July 2003. Although her body was never recovered, police found her blood in the back cabin.

They also found the blood of another, still-unidentified person – the first clue that Arizmendi may not have been the only woman Howell hurt – along with a rock and steak knife streaked with what appeared to be blood, according to court documents.

A sex tape stashed in the van shows scenes involving at least two other women, the documents say. Their identities – and their fates – remain a mystery.

Howell was working odd jobs in Connecticut when Arizmendi disappeared – cutting grass in Wethersfield, Hartford, New Britain and West Hartford.

Ana McBride said Howell lived on her street New Britain for a short time and knows the family of an already-named victim.

"He was like an ordinary person but just like, creepy, a little bit mysterious, wasn't social," McBride said. "I told my mom, I said, 'We have to thank God, because it could have been me or her,' you know? That's very scary."

Sometime after Arizmendi vanished, Howell made his way to Virginia. He was taken into custody as a fugitive from justice almost exactly 10 years ago and was charged with Arizmendi’s murder, affidavits reveal.

According to court documents, he started opening up to another inmate at the Cheshire Correctional Institute while awaiting trial.

Howell told cellmate Thomas Rodrigues Jr. that he "wanted a speedy trial because the state’s case against him was circumstantial" and that "the state didn’t have a body and he didn’t want the body to show up because it would do him in," affidavits allege. He also told Rodrigues he had beaten up Arizmendi in his van, "breaking her nose and getting blood all over the place."

Police believed Arizmendi suffered a "very violent death," according to court documents.

Affidavits show Rodrigues took notes on his conversations with Howell and relayed the information to authorities. He was expected to be a witness during Howell’s trial, but the trial ended when Howell pleaded guilty under the Alford doctrine to the lesser charge of manslaughter.

Later on, Howell tried unsuccessfully to withdraw his plea, claiming the public defender gave him only five minutes to decide whether to accept the offer, court documents say.

He was arrested for witness intimidation in 2007 after calling Rodrigues a "snitch" and threatening to kill him and his family, according to the documents. Howell was convicted two weeks later.

He’s no stranger to the legal system. Court records show Howell has numerous felony convictions in Virginia, including larceny and burglary, and has also been arrested in Georgia and New Jersey.

Now sources say he could hold the key to a case that's been shrouded in mystery since 2007, when investigators dug up the first three sets of remains buried behind that strip mall in New Britain.

Four of the victims have been identified – Diane Cusack, Mary Jane Menard, Joyvaline Martinez, and, most recently, Melanie Camilini – but at least three other bodies, for now, remain nameless.

Investigators haven't publicly named Howell, but said they've identified a suspect, a person who no longer poses a threat, and that charges are forthcoming.