By Greg Argos

PHILADELPHIA (CBS) — Police are investigating the disappearance of a man in the city’s Frankford section. Authorities are now questioning a man about the disappearance.

The focus of the investigation is on Fillmore Street in Frankford. Police have not released much information, but crime scene investigators are inside the apartment on the 1600 block of Fillmore Street. Police say it’s all tied to a missing persons investigation.

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Family and friends have shared a flier with Eyewitness News and police confirm this is the man who was reported missing.

Credit: CBS3

70-year-old Robert Derer was last seen Monday evening. Around 1 p.m. on Thursday, family members filed a missing person report and police arrived to the apartment and noticed blood on the door.

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Eyewitness News is told the missing man’s roommate — a 28-year-old man — was home. Investigators confirm the roommate is being questioned by police.

Meanwhile, a search warrant was issued and police entered the building around 8 p.m.

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Crime scene investigators have arrived and we’re waiting to hear more information about what may have happened inside.