Haro is suspected of ordering the hit, which Garrett Warren miraculously survived, despite being shot four times outside his California home in May 2000.
She was arrested on July 13 by police who released her two days later. She didn't have to post bail because of an "insufficient complaint."
Authorities are now searching for more evidence against Haro - who was known to have been involved in a custody dispute with Warren over their daughter Kyla.
While Haro was in jail, Warren obtained temporary custody of Kyla.
A sheriff's department spokesperson says, "The charges have not been dropped against Ms. Haro, but more information is needed to proceed in this case. Ms. Haro could be re-arrested at any time."
Despite divorcing Haro in 1992, Pesci - who has a child with Haro - is reportedly devastated by the claims.
A source tells The National Enquirer, "Joe is devastated. He knows Marty is not capable of hurting anyone and certainly wouldn't know how to arrange a hit. Joe says he'll do whatever he has to do to help her out of this mess, even testify in court."
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