Sources: Pennsylvania trooper shooting suspect detailed ambush in letter

Eric Matthew Frein is wanted in connection with the shooting of two Pennsylvania State troopers at the Blooming Grove station on Friday, Sept. 12, 2014.

(CNN) -- A handwritten letter thought to have been written by the suspect in the September 12 ambush of two Pennsylvania State Police troopers details how he shot the officers and then escaped, two senior law enforcement sources with knowledge of the investigation told CNN on Monday.

The letter, which authorities found during the manhunt for Eric Matthew Frein, does not offer a motive for the shooting, according to the sources.

Authorities aren't sure if the letter was left on purpose or by accident, and it's unclear when or why the letter was written. But based on details contained in it, authorities think it was written by Frein, the officials said.

Frein, 31, is suspected in the September 12 ambush that left Cpl. Byron Dickson dead and another trooper wounded outside the Pennsylvania State Police barracks in Blooming Grove, Pennsylvania. He is still being sought.




CNN's Shimon Prokupecz contributed to this report.