The court in Mönchengladbach will hear charges that the three men aged between 21 and 54 killed the 89-year-old woman to get at money stashed in her house.
They made up a story to get her to let them into her house before pushing her down the stairs and strangling her with a bicycle brake cable, the prosecutors allege.
When police started looking for the woman, the accused took her body, which they had hidden in a garage, and put it in a rain water barrel and poured quicklime on it.
When this did not dispose of the body, they tried to sink it in a lake, but it floated to the surface.
It was found by investigators after one of the charged men admitted his part in the killing and took them to the lake.