Jurors heard closing arguments today in the second murder trial of Wilfredo Santiago in the execution style slaying of Police Officer Thomas Trench in 1985.

The panel began deliberating the case shortly after 4 p.m.

In their closings, both the defense and the prosecution focused on the credibility - or lack thereof - of witnesses who have taken the stand since testimony began May 1.

Many of the witnesses have changed stories, altered details or contradicted themselves altogether in statements and testimony at other proceedings in the last 23 years.

There is no physical evidence nor eyewitnesses linking Santiago to Trench's killing and the prosecution's case has been mostly circumstantial.

It has argued that Santiago shot Trench, 43, in the face and neck as he sat in his patrol car at 17th and Spring Garden Streets in a case of mistaken of identity. Officials contend Santiago had a grudge with another officer who had been driving the same patrol car in the previous shift and was seeking vengence.

Defense attorney David Rudolvsky argued that because of the grudge, investigators zeroed in on Santiago from the start and have repeatedly shaped their case to fit that theory.

He said three jailhouse witnesses who claimed they heard Santiago admit killing Trench had many reasons besides the truth to testify that way.

Assistant District Attorney Carlos Vega sought to portray two of the jailhouse witnesses, a robber and a murderer who have served their prison terms, as seeking to redeem themselves by telling the truth.

He also made an emotional appeal on behalf of Trench's survivors and the officer who was Santiago's alleged target and remains on the force.

Vega told the jury that a conviction would tell the officer, "No, it's not your fault."

In the end, it appeared the only witnesses whose testimony was not suspect included the medical examiner, a police ballistics expert and a crime lab technician, none of whom could pin the crime on Santiago.

Vega, in seeking to bolster one jailhouse witness, went so far as to say a murderer was more credible than the former public defender - now a sitting judge - who had been called to discredit the testimony of another jailhouse informant.

The defense rested Friday after raising the possibility that Trench, who was shot and killed May, 28, 1985, was slain in retaliation for the bombing of the MOVE compound that claimed the lives of 11 people two weeks earlier.

A jury convicted Santiago, now 44, in 1986, but an appeals court ordered a new trial in 1991 because of judicial conduct. The first scheduled retrial was called off when a judge ruled the prosecution's conduct in the first trial was so egegious that it would be wrong to subject Santiago to another proceeding. An appeals court overturned that decision in 1994, but a series of appeals an motions delayed the retrial until this year.

Contact staff writer Joseph Gambardello at 215-854-2153 or jgambardello@phillynews.com