Taiwan maintains the death penalty for murder, but Koon said Chan was unlikely to get that if he voluntarily surrendered.
The revelation comes as Hong Kong is bracing for a 20th consecutive weekend of protests.
Police on Friday rejected an application for a large rally on Sunday saying they feared hardcore protesters would hijack it and turn violent.
The application was made by the Civil Human Rights Front, a group that advocates non-violence and which organized marches earlier in the summer where millions hit the streets.
The CHRF’s leader Jimmy Sham was hospitalized on Wednesday after he was attacked by men wielding hammers.
While the CHRF’s rallies have begun peacefully, masked protesters have routinely clashed with police later on.
Previous protest rejections by police have been widely ignored by protesters and quickly turn violent.
Hardcore protesters have embraced vandalism and throwing petrol bombs, while riot police respond with volleys of tear gas, rubber bullets and, more recently, live rounds.
Protesters are demanding an independent inquiry into the police, an amnesty for those arrested and fully free elections, all of which have been rejected by Beijing and Hong Kong’s unelected leader.