NEWARK, N.J. (CBSNewYork/AP) – Testimony has begun in the lawsuit against a Newark school district stemming from the 2007 execution-style schoolyard killings that left three college-bound friends dead.

The suit, brought by the families of the victims and a fourth victim who survived the attack, claims the Mount Vernon School was negligent by leaving the playground open at night when it was a known gang hangout.

According to the lawsuit, the school’s security cameras did not work and the playground was poorly lit.

A Newark detective testified on Tuesday that the bullet marks on a door were made from gunshots fired on school property.

Dashon Harvey, Iofemi Hightower and Terrance Aeriel were killed on Aug. 4, 2007. Six men and boys arrested for the murders have pleaded guilty or been convicted and are serving combined sentences of more than 1,000 years.

The families are seeking millions in damages from the school district, former school superintendent Marion Bolden and the state, which took over the Newark schools years ago.

In an earlier criminal trial for one of the defendants, the lone survivor of the attack testified that she was sexually assaulted, slashed with a machete and shot in the head.

Prosecutors said several of the defendants were engaging in an initiation ritual for members of the MS-13 street gang. The men did not know the victims, prosecutors said in earlier trials of the defendants.

The four victims, who attended or planned to attend Delaware State University, were hanging out listening to music behind the school on the night of Aug. 4, 2007, when they were approached by the suspects, who robbed them and forced them to lie on the ground before shooting them, according to prosecutors.

The final defendant who was convicted or pled guilty to the murders was sentenced last week to nearly 200 years in prison.

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