MONROE COUNTY -- State police believe Eric Matthew Frein is hiding in the woods of Monroe and Pike counties.
They believe he is armed, has perhaps booby-trapped the woods, and may be behaving like a sniper.
Investigators said they have already found and seized an AK-47 and ammo from the woods, as well as food supplies and several pipe bombs.
State police say they have found soiled diapers, which they believe Frein is using to stay in one position for long periods of time.
Search warrants revealed state police also found and took a manual from Eric Frein's bedroom, titled "Sniper Training and Employment."
A book by that title obtained by Channel 16 reveals information Frein may be using in the woods, including the fundamentals of sniper field techniques.
There is a section on camouflage that describes how best to avoid detection including the three basics: hiding, blending, and deceiving, or tricking the enemy into false conclusions about the sniper's location.
The book advises on how to work with difficult terrain, which is exactly how state police describe the area where they think Frein is hiding.
It describes how to create sniper positions by digging tunnels and creating other shelters.
The book describes how the sniper should avoid walking upright by either crouching or crawling.
There is also a section dedicated to ambush attacks and counter-sniper operations.
Marksmen have been brought in to search for Eric Frein with sniper-style weapons and according to the book, a sniper should identify the routines of his enemy, determine patterns, and then plan the best time and location to "...engage the enemy sniper."
The book stresses the importance of a sniper researching the area he will be using to hide, using maps and other points of reference.
Investigators said Frein knows the woods around his home very well.
The book also refers repeatedly to a sniper team, which is the most ideal way to work with a partner.
At this point, state police say they have no reason to believe Frein is acting with anyone else.