ISTANBUL — Defendants facing lengthy prison sentences for allegedly trying to overthrow the Turkish government with an environmental protest and their supporters said on Tuesday they expect a verdict in the long-running trial soon and accused the government of using the case to criminalize opposition voices.

A prosecutor last week asked the Istanbul court in a formal legal opinion to sentence three of the 16 defendants to solitary confinement for the rest of their lives for allegedly organizing demonstrations in 2013 to save central Istanbul’s Gezi Park, where the government wanted to build a shopping mall. At least eight people were killed in the police crackdown.

Six others, including a filmmaker, lawyer and professor, face up to 20 years in prison for aiding and abetting the alleged wrongdoing, while the prosecutor wants the case files for seven defendants who have fled overseas to now be separated from the main trial. All the defendants are terrorism suspects, he argued.

They deny the charges, contending that the protests against then-Prime Minister Recep Tayyip Erdogan’s government that spread to all but one province in the country was too large and dispersed for any one group or individual to start or stop it.