Anger over a lack of pay raises, increasing costs of healthcare and the amount of money Mesa has spent to retain the Chicago Cubs led a city employee last Friday to attempt to sabotage public wastewater-treatment operations at a plant in Gilbert, according to court documents released Monday.

After surrendering to Gilbert police about 4:30 a.m. Friday, Robert Anthony Olson, 43, admitted to investigators that he manually shut down numerous valves to nine critical components of the plant at 4400 S. Greenfield Road.

Gilbert SWAT team responds to standoff at plant

His goal, police said, was to create a buildup of methane gas that could have caused an explosion "destroying a quarter city-block," court documents state.

Olson "believed his actions were justified because the city of Mesa management needed to know that the employees have power," police state in the new report.

Particularly, Olson was angered that employees have repeatedly gone without pay raises, while having to pay more in healthcare premiums. Olson was also angered over how much money the city has spent to keep the Cubs from relocating from Mesa to Florida.

No damage was caused to the system and safety mechanisms vented the methane gas to ensure it didn't reach critical levels, Ian Satter, a Mesa spokesman, said last week.

Olson was initially employed by Mesa from December 2001 to October 2002. He then left the city, taking jobs in Phoenix and Avondale before returning to Mesa as a wastewater-treatment plant operator on Sept. 3, 2007, according to Mesa officials.

Olson successfully passed an FBI and other background checks when rehired by Mesa.

Olson was the lone employee on the midnight shift Friday when he began shutting down the plant, which is owned by Mesa, Gilbert and Queen Creek but operated by the Mesa Water Resources Department.

About 2:30 a.m., Olson called 911, telling police that methane was building within the plant and that he was armed with a knife and handgun, court documents state.

Gilbert SWAT officers and Mesa police responded to the scene and began negotiating with Olson to surrender, which he did about two hours later.

He was booked into the Maricopa County 4th Avenue jail on charges of terrorism, making terrorist threats, misconduct involving weapons, tampering with a public utility, criminal trespassing and criminal damage to property.

FBI officials assisted with the investigation because of the terrorism charges, but opted to have the matter prosecuted in state court, said Special Agent Manuel Johnson, a FBI spokesman.

Olson had his initial court appearance from his jail cell Monday morning. He is being held on $250,000 bond.