A letter sent to an inmate in Beaver County may hold the key to the mysterious Mother's Day fatal shooting of ex-teacher Rachael DelTondo in Aliquippa, Pa.

Beaver County District Attorney David Lozier is taking the letter so seriously, the inmate it was addressed to has received a generous plea deal on assault and robbery charges in exchange for testimony about the letter sent to him in jail, TribLive.com is reporting.

The letter alleges that a police officer shot and killed former elementary school teacher Rachael DelTondo, 33, as she stood in front of her mom's Aliquippa home on the evening of May 13.

DelTondo was shot at least 10 times at close range in a case that has already generated major shock waves within the Aliquippa Police Department.

But the shooter in the case has remained a mystery, and no suspects have been publicly identified.

Now comes the letter to inmate Wayne Cordes, 21, of Aliquippa.

TribLive reports it was "allegedly written by somebody outside the jail and identified a police officer as having committed the homicide." This, according to the Beaver County DA.

Facts from TribLive.com:

DA Lozier wouldn't identify the alleged writer of the letter. He also declined to say whether the letter identified the officer or for which department the officer worked.

However, the recipient of the letter, Wayne Cordes, was arrested in the assault and robbery case by Aliquippa police Sgt. Kenneth Watkins. Under the plea reached Monday, Cordes is getting off on single counts of misdemeanor simple assault and misdemeanor theft.

Watkins, meanwhile, was placed on administrative leave in the wake of DelTondo's murder because his 17-year-old daughter, Lauren, was with DelTondo minutes before the killing.

DelTondo, Lauren Watkins and 25-year-old friend Tyrie Jeter went out for ice cream earlier that night.

Lauren Watkins dropped off DelTondo at her mother's Buchanan Street home at 10:44 p.m. Four minutes later, police received 911 calls reporting shots had been fired.

Amid the case, Aliquippa Chief Donald Couch was placed on leave for unspecified reasons, and Assistant Chief Joseph Perciavalle III was named acting chief.

But Perciavalle was suspended two days later when authorities said he'd sent explicit sexual material in a group message that included Lauren Watkins. Those charges stemmed from a text message conversation in May that came to light after Lauren Watkins turned over her cellphone to Aliquippa police as part of the investigation.

Since then, acting Aliquippa police Chief Robert Sealock recused the department from the DelTondo investigation, providing no reason but pledging to help the investigating agencies.

The investigation continues, now overseen by the Beaver County DA.