PHILADELPHIA (CBS) — The suspect accused of murdering four young men and burying their bodies on his property in Bucks County is claiming he has killed before.

According to Philadelphia Police sources, Cosmo DiNardo has apparently confessed that he was involved in at least two other killings in Philadelphia in the last five years.

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Sources say the department is actively investigating DiNardo’s claims made in that confession to Bucks County investigators.

It was a plea deal that spared him from inevitably facing the death penalty.

Spokesmen with Philadelphia Police and the Bucks County District Attorney’s Office had no comment.

Jimi Patrick, Dean Finocchiaro, Tom Meo and Mark Sturgis were each shot and then buried after police say DiNardo lured them to the property under the guise of a marijuana transaction.

DiNardo apparently made violent threats over social media ahead of the killings that began just after July 4.

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A childhood friend posted to Facebook: “I grew up with Cosmo, we were best friends since the fourth grade but grew apart due to his recent health struggles. Unlike people who are passing judgement, I watched him change and struggle with his mental health. He was never the same after his (ATV) accident. The Cosmo I knew for over 10 years would never be capable of anything like this.”

DiNardo’s cousin, Sean Kratz, has also been charged in the murders.