BRIDGETON, NJ  — Authorities are still looking for guns in four state prisons where security has been increased because of a threat of armed uprisings.

Corrections officers continued searching South Woods State Prison in Bridgeton and three other institutions after finding letters Sunday afternoon in a Rahway prison cell that indicating uprisings were being planned.

So far, authorities are treating the letters seriously. The inmate now believed to be the author of all three, convicted murderer Lester Alford, is named by authorities as a top regional leader in the Bloods, a powerful street and prison gang.

Officers found the letters on Alford while he was in a cell separate from the general population at East Jersey State Prison after being found in possession of a cell phone, according to corrections officers familiar with the case.

A female friend from outside the prison contacted authorities Sunday to inform them Alford had text-messaged her from a cell phone, but investigators now believe it was another inmate because Alford was isolated, according to Tom Moran, head of the union representing corrections sergeants. Officers searched Alford in his isolated cell and did not find another phone, but they turned up the letters.

The letters, signed with three different nicknames, detail plans for simultaneous uprisings at South Woods, East Jersey, Northern State Prison in Newark, and New Jersey State Prison in Trenton. They include claims to have 13 guns, an unspecified total number of cell phones, and men in place at each prison prepared to lead armed revolts.

One letter details numbers of officers and civilian personnel, locations of offices, bathrooms and labs, and the methodology of an electronic system used for locking units in South Woods' medical unit, where one uprising would take place. Alford has never served time in South Woods, according to Joe Malagrino, head of the largest corrections officers union.

Another letter also mentions plans to kill Newark Mayor-elect Cory Booker after the prison uprisings.

Department of Corrections spokeswoman Deirdre Fedkenheuer declined comment on the letters' details Wednesday because the investigation had not yet closed.

Initially, it was unclear whether Alford had written or received the letters. An online memo from a union official to officers erroneously listed his nickname as Fruit, which is actually the listed name of a recipient of one of the letters.