Two police officers are under investigation over "distressing" messages relating to the fatal Shoreham Airshow crash.
Sussex Police said a private message had allegedly been sent online to a colleague about the force's response to the disaster.
The recipient immediately reported the incident and the two officers, both of whom are based in Brighton and Hove, are now being investigated for gross misconduct by the Professional Standards Department.
The force's deputy chief constable Olivia Pinkney said: "I cannot emphasise how upset I am that we are investigating such an allegation.
"My colleagues have informed the victims' families and apologised to them for the unnecessary distress it will undoubtedly cause them.
"They are disappointed as we all are. Such an allegation impacts on everyone who was affected by the crash and detracts from the professionalism of hundreds of colleagues who have worked so tirelessly on this operation."
11 people were killed after a vintage jet crashed on to the A27 in West Sussex on 22 August.