The Shovel

Alison's Murder Weapon is a shovel that was discovered by The Liars in Over My Dead Body. It was planted by "A" in a grand plan to set-up the girls. The shovel is currently evidence in Alison DiLaurentis' "murder" case.

About
On the day of Alison's death, she is She is hit in the back of the head with the shovel possibly in an ambush or attempt to get away from her killer, and then buried alive with it. After, the shovel is somehow obtained by "A."

Season 2
In Over My Dead Body, Emily sees a rusty curved shovel perched on the barn door and affirms that the shovel must had been placed there recently. Spencer picks it up to see a note taped to the inside of the shovel, with latitude and longitude coordinates left by "A". The girls use the shovel to dig up Dr. Sullivan, who they thought had been buried alive before helicopter begin to roar above them.

In the investigation room, Detective Wilden confronts the girls, and asserts that he has caught the girls with the murder weapon, which the police have known about all along. He puts the now-bagged shovel from the barn on the table.