PHILADELPHIA (CBS/AP) — A pot dealer who confessed to killing four men on his family’s Pennsylvania farm also claimed to have killed two people in Philadelphia, but the city’s police commissioner called the information “sketchy.”

City detectives are looking through their files to check on the claims made by 20-year-old Cosmo DiNardo, but they have not had a chance to question him, Philadelphia Police Commissioner Richard Ross said Tuesday.

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“We have to talk to him directly in order to have a starting point,” Ross said. “Dealing with it third-hand is virtually impossible.”

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Philadelphia police told CBS3 that DiNardo apparently confessed that he was involved in at least two other killings in Philadelphia in the last five years.

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

DiNardo was charged last week in neighboring Bucks County with four counts of first-degree murder in the case of four missing men whose remains were found on his parents’ farm. He also claimed that he killed a man and a woman in Philadelphia years ago but did not know the names of those victims, Ross said.

Philadelphia police said Bucks County authorities are still investigating DiNardo’s statements. The Bucks County district attorney declined to comment beyond court papers released last week, which don’t mention the Philadelphia claims.

DiNardo told authorities that he lured the four men to his family’s 90-acre farm under the guise of marijuana transactions before killing them there, according to the court papers. One man was last seen July 5, and the other three vanished two days later.

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The bodies of three of the men were placed in an oil tank that was converted into a cooker that DiNardo called the “pig roaster,” according to court papers. He doused them with gasoline and lit them on fire before burying them more than 12 feet deep, investigators said.

Authorities found the body of the fourth man, 19-year-old Loyola University of Maryland student Jimi Taro Patrick, in a separate grave on a remote part of the farm after DiNardo told police where he buried him.

In exchange for that information, prosecutors agreed not to seek the death penalty.

DiNardo’s 20-year-old cousin Sean Kratz is also charged in three of the killings.

Both he and DiNardo are being held in jail without bail.

DiNardo’s lawyers say he is remorseful, and he told reporters last week that he was sorry.

Kratz doesn’t have an attorney, according to online court records. His mother declined to comment on the accusations last week.

The other victims are 19-year-old Dean Finocchiaro, 22-year-old Mark Sturgis and 21-year-old Tom Meo.

Sturgis’ family has hired a law firm to investigate whether other people besides DiNardo and Kratz are civilly responsible for the deaths, according to a statement from the firm.

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