Anabaptist covers such a large and varied group of people that it would be much easier to speak of specific groups and circumstances. Which death sentences are you thinking of?
Those carried out throughout both Roman Catholic and Protestant states in the 1500's.
Here is a quote from
The Rise of the Radical Anabaptists
The treatment of the Anabaptists is a great blot on the page of the Reformation, Strassburg being the only center that tolerated them.[24] Grebel and Manz were not the only ones to be persecuted. Six executions in all took place in Zurich between 1527 and 1532. The last executions took place March 23, 1532, when Heinrich Karpfis and Hans Herzog were drowned. Blaurock was scourged, expelled, and burnt in 1529 at Clausen in the Tyrol. Haetzer, who fell into carnal sins, was beheaded for adultery and bigamy at Constance, February 24, 1529. Huebmaier, who had fled from Waldshut to Zurich, December, 1525, was tried before the magistracy, recanted, and was sent out of the country to recant his recantation.[25] He labored successfully in Moravia, but was burnt at the stake in Vienna, March 10, 1528. Three days afterwards his faithful wife, whom he had married in Waldshut, was drowned in the Danube.
Other Swiss cantons took the same disciplinary measures against the Anabaptists as Zurich. In Zug, Lorenz Fuerst was drowned, August 17, 1529. In Appenzell, Uliman and others were beheaded, and some women drowned. At Basle, Oecolampadius held several disputations with the Anabaptists, but to no avail. The Council there banished them with the threat that they should be drowned if they returned (November 13, 1530). The Council of Berne adopted the same course.
In Germany and in Austria the Anabaptists were persecuted still worse. In April of 1529 the Diet of Speier decreed that, "every Anabaptist and rebaptized person of either sex be put to death by sword, or fire, or otherwise." The decree was severely carried out, except in Strassburg and the sphere of influence of Philip of Hesse, where they were treated more leniently.
They were treated most horribly by the Roman Catholic countries. In Goerz the house in which the Anabaptists were assembled for worship was set on fire. ““In Tyrol and Goerz,” says Cornelius, "the number of executions in the year 1531 reached already one thousand; in Ensisheim, six hundred. At Linz seventy-three were killed in six weeks. Duke William of Bavaria, surpassing all others, issued the fearful decree to behead those who recanted, to burn those who refused to recant...throughout the greater part of Upper Germany the persecution raged like a wild chase...the blood of these poor people flowed like water so that they cried to the Lord for help...but hundreds of them of all ages and both sexes suffered the pangs of torture without a murmur, despised to buy their lives by recantation, and went to the place of execution joyfully and singing psalms.””[26]
Though physical persecution took place from the State against the Anabaptists, individual Reformers, though not lifting the abuse of the sword upon these people, disagreed with the persecution but retained the title of “heretic” upon them.[27] Luther said, “The devil, on the contrary, disorganizes and ruins everything through his factious and disturbing spirits, his ratling and boisterous servants, in the external and worldly government and life as well as internally in the hearts of men, whom he really makes insane and blind by his evil spirits, as we now have experienced with his insurrectional prophets, fanatics, and Anabaptists.”[28] Calvin called them, “furious madmen,”[29] “supercilious,”[30] and “delirious.”[31] However, Calvin was used as a means to convert many Anabaptists (those who were wisely tolerated in the territory of Strassburg while Calvin was present there for three years) and they brought to him from the city and country their children for baptism.[32]
