PHILADELPHIA (AP) _ A grand jury will investigate the deadly collapse of a nightclub pier along the Delaware River to determine whether criminal charges should be filed, city officials said Friday.

Three women were killed and dozens of others injured May 18 when the pier supporting the week-old open-air nightclub Heat broke apart and plunged about 40 people into the dark, murky water.

Investigators were supposed to release preliminary findings Friday on the cause of the collapse, but District Attorney Lynne Abraham asked that the report be withheld to avoid prejudicing the grand jury, mayoral spokeswoman Barbara Grant said.

``We've been asked by the D.A. to cooperate with the grand jury investigation, and obviously we're happy to do that,'' she said.

Investigators have been looking into whether pier owner Michael Asbell and nightclub owner Eli Karetny knew the 91-year-old pier was unstable days before the collapse.

Commerce Construction Corp. president Terry Zettle has said his company had told the nightclub that the foundation was slanting and metal supports were twisted. The company had been hired May 15 by Karetny to look into cracks in the concrete surface of the pier, Zettle said.

``We were amazed that they had people on that pier after we told them of what we found,'' Zettle said.

Attorneys for Asbell and Karetny did not immediately return calls Friday.