BERLIN, Germany (CNN) -- Five senior citizens are behind bars in Germany after they allegedly kidnapped and beat a man because he owed them money, police in southern Germany said Wednesday.
Police say the victim, a U.S. citizen born in Germany, was involved in helping the suspects invest large amounts of money in overseas organizations. The details of those transactions were still unclear, police said.
Two of the suspects kidnapped the 56-year-old man from his home in Speyer, near Heidelberg, last week, police said, tying him up with electrical tape and taking him to a town in southern Germany.
The victim had "obviously been beaten and had two broken ribs," police added.
The men -- a 74-year-old German and a 60-year-old American -- then stuffed their victim in the trunk of the older man's car and drove him to a house in Chieming, on Lake Chiemsee in Bavaria, police said.
For the next four days they kept the victim in the cellar of the house and gave him no opportunity to make contact with the outside world, police said.
"An attempt to escape after asking for a cigarette didn't work," police said.
The man's break came when he was allowed to make a telephone call in order to raise money for his release, police said. That allowed him to make his situation known, police said.
Around 4 a.m. Saturday night (10 p.m. ET Friday), "a special police unit from Munich stormed the location in Chieming from all sides where the hostage was believed to be held," police said. They found the victim in a cellar, "lightly injured," police said.
They arrested five suspects: the two men, the 79-year-old wife of one of the men, and another couple, believed to be in their 60s.
All five are accused of having threatened the victim with death, said Volcker Ziegler, the public prosecutor for the city of Traunstein, near Chieming. They told him "that he would stay imprisoned until he had given them money," Ziegler said.
The five suspects supposedly invested large amounts of money overseas that they wanted to get back from their victim, Ziegler said. The couple who owned the house in Chieming wanted $2.4 million, the 60-year-old American wanted $662,000, and the other couple hoped to get $300,000, he said.
The investigations were ongoing, he said, but all financial transactions are believed to have taken place in the United States.
All five suspects went before a judge Sunday and were charged with taking part in kidnapping, which in Germany carries a prison sentence of between five and 15 years, Ziegler said.
They remain in custody, police said.