Story highlights Letter details shooting and immediate aftermath, law enforcement officials tell CNN

It's not clear whether suspect Eric Matthew Frein left the letter on purpose or not

It doesn't offer a motive

Frein is wanted in last month's ambush shooting of two Pennsylvania state troopers

A handwritten letter thought to have been penned by the suspect in last month's ambush of two Pennsylvania State Police troopers details how he shot the officers and then escaped, two senior law enforcement officials in Pennsylvania 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 officials.

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.

State police spokesman Trooper Tom Kelly issued a statement Monday saying that he could not confirm any information provided by unnamed sources.

Frein, 31, is suspected in the September 12 ambush that left Cpl. Bryon Dickson dead and Trooper Alex T. Douglass wounded outside the Pennsylvania State Police barracks in Blooming Grove, Pennsylvania.

A massive search for Frein followed, at times involving as many as 1,000 officers. Despite sightings and other leads, he has not yet been caught.

Authorities previously said that a review of a computer hard drive used by Frein showed that he had planned the attack for years.

Frein has been described as a survivalist and military reenactment enthusiast with a hatred for law enforcement, authorities say.