The four-alarm fire that burned through a century-old estate in Shrewsbury on Monday was caused by fireplace ashes that had been "improperly disposed," according to the Monmouth County Prosecutor's Office.

The fire, which was ruled accidental, originated in a hall closet on the first floor where still-burning ashes cleaned from a fireplace had been placed, according to Charles Webster, a spokesman for the prosecutor's office.

Shrewsbury Fire Department Chief Peter Gibson said that the call came in around 1:15 p.m. Feb. 4 for a fire at 469 Sycamore Ave. When firefighters arrived, "There was heavy fire showing on the first floor," he said.

The cause of the fire was investigated by the prosecutor's office in conjunction with the county fire marshal and local fire officials, Webster said.

Volunteer firefighters and emergency rescue squads turned out from Shrewsbury, Northside (Tinton Falls), Little Silver, Red Bank and Eatontown.

The 7,042 square foot estate dates back to the late nineteenth century and according to county property tax records was owned by Jeffrey and Joan Rich. In 2012, it was assessed for $1,057,000.