Police in Italy have arrested two American students.
They the pupils are connected to the killing of a policeman in central Rome.
According to a statement from Italian military police Carabinieri, the students are also being held for attempted extortion.
The students allegedly stabbed 35-year-old Mario Cerciello Rega to death on Friday.
Another police officer was injured in the incident.

US, Iran conclude high-level talks in Switzerland, mediators say
Vance hails 'historic' first meeting in US-Iran peace talks in Switzerland
54 injured, 18 missing after explosion at Qatar LNG site, authorities say
Israeli fire kills nine people in Gaza
Europe braces for prolonged heatwave as temperatures approach 40C