PCC Nick Alston said "investigations into the murders of James Attfield and Nahid Almanea in Colchester" in 2014 had cost £2.6m.
A 16-year-old boy is being held over the killing of Mr Attfield, who was stabbed 102 times, and Ms Almanea, who was found with 16 knife wounds.
Mr Alston now plans to close 50 of the 80 buildings the force owns.
He also confirmed the force's Chelmsford headquarters would be moved, after admitting general reserves "are now the lowest in the country".
Mr Alston told the Essex Police and Crime Panel a provisional budget overspend of £2.1m was to be included in the new budget.
Government help had been "unfortunately refused" but Home Secretary Theresa May was told the force's finances are in a "perilous state", he said.
"It is lower than Bedfordshire, which held a referendum to raise the precept above the maximum level of 2%," Mr Alston said.
However, he does not support the idea of a referendum in Essex because it would cost £2m and would almost certainly would be voted down.
The force had already made savings of £9m this year and cut the number of officers by 110.
More savings could be achieved by moving to a new headquarters, basing most police officers in hubs and establishing a number of small community police stations.
Mr Alston said the number police stations with public counters could be reduced.
Police reserves currently held are £18m but by March 2016 are forecast to fall to £14.1m.
Treasurer Charles Garbett told the panel if the reserves go down to £10m the police will have problems with capital expenditure and dealing with one-off events.
Two murder investigations led Essex Police to overspend on its budget last year by more than £2m.