CHICAGO – Videotapes of angry officers savagely beating civilians and charges that a murder plot was hatched within an elite special operations unit have Chicago’s troubled police department reeling again.

Fueling the department’s woes is word from federal prosecutors that they are investigating claims that homicide detectives tortured suspects into confessing to murders that landed them on death row in the 1980s.

Not since club-swinging cops in baby-blue helmets chased demonstrators through clouds of pepper gas at the 1968 Democratic National Convention have Chicago police been so awash in troubles.

The biggest shock came Wednesday when federal prosecutors charged special operations officer Jerome Finnigan with planning the murder of another member of the unit to keep him from talking to the government.

“This kind of stuff on Page One is just horrible,” and reinforces a misleading stereotype of police, said Roosevelt University political scientist Paul Green, who taught at the police academy for four years.

“The overwhelming 99.9 percent do their job professionally,” he says.

But evidence of deep-rooted problems is piling up.

Finnigan, 44, is one of six members of the special operations unit, created to crack down on gangs and drugs, charged with operating a shakedown operation aimed at civilians. Prosecutors say they have him on tape weighing the possibility of having someone kill a fellow special operations officer to keep him from becoming a witness against him.

Finnigan and his attorney, Michael Ficaro, declined to comment.

In July, three off-duty officers pleaded not guilty to charges that they had beaten four businessmen in a bar in a videotaped confrontation.

In another videotaped confrontation, off-duty officer Anthony Abbate was seen apparently beating a 115-pound female bartender because she would not serve him another drink. Abbate, who originally was charged with a misdemeanor, has pleaded not guilty to a felony charge of aggravated battery.