DOUGLAS — State Police detectives have taken possession of items that a Douglas woman took from the Florida trailer of convicted killer ­Rodney Stanger and that she believes might hold clues to other unsolved slayings.

Bonnie Kiernan — sister of Stanger’s longtime girlfriend, Chrystal Morrison — said that detectives arrived at her home about 11 a.m. Tuesday and seized all of the items she collected last month from his trailer in Summerfield, Fla. Those items include a 2000 Massachusetts firearm identification card with a photo of Stanger. It looks remarkably like the man in a sketch who was spotted in the area of Comins Pond in Warren the day before lifeguard Molly Bish disappeared.

The card had been renewed two months before Bish was ­abducted and killed.

Stanger is serving 25 years in prison for the murder of Morrison in 2008. Kiernan told police back then that she had been given a cryptic message during a phone call from her sister that indicated Stanger may have been involved in killings in Massachusetts.

She alluded to Bish and ­Holly Piirainen, who was ­abducted in 1993 in Sturbridge.