His trial and execution are described on this site:
A document of c.1587 mentions that John Sandys, tried at the Gloucester summer assizes in 1586, was condemned to death by Sir Roger Manwood. There are no Assize Records for the Oxford Circuit, to which Gloucester belonged, prior to 1627 but it is clear that Sandys was charged under the Statute of 1585 'against Jesuits and seminary priests and such other disobedient persons'. This made it an offense for an Englishman ordained abroad to come into, or remain in, England. Found guilty, he was sentenced to be hanged, drawn and quartered.
The sentence was carried out at Gloucester on April (sic: should be August) 11th 1586. In the morning he was able to celebrate Mass and he made 'a very fervent and forcible exhortation to many Catholics there present in secret, for their perseverance in the Catholic faith'. Then word came that the officers were at the prison gates to take him to the place of execution: 'desiring their patience a little (he) ended his service, blessed and kissed the company and so departed to his martyrdom'. Another account mentions 'as he was at his 9 howert or thereabout, word was brought that the executioners staid for him at the prison gate'. This suggests that Sandys was reciting the canonical hour of None, the last of the Little Hours of the Divine Office.
Contemporary accounts of the execution show a combination of inefficiency and deliberate cruelty which made the onlookers protest. There was great difficulty in finding an executioner and even in procuring a knife with which to carry out the drawing and quartering of the body demanded by law:
'At last thay found a most base companion, who was yet ashamed to be seen in that bloody action, for he blacked and disfigured his face, and got an old rusty knife full of teeth like a sickle, with which he killed him'.
In spite of the promise of the Sheriff, Paul Stacy of Stanway, that he would be allowed to hang until dead, he was cut down as soon as he was cast off the ladder. His clothes were then removed and by the time this was done he had recovered consciousness and while being disembowelled he was even able to struggle with the executioner and to grasp the knife. The butchery was such that the people present protested and some Protestant clergymen condemned it in their sermons. As he suffered, Sandys 'cried out ever with St. Stephen "Lord forgive my persecutors" and so fell asleep in Our Lord'.
The Diocese of Shrewsbury also honors him; he was beatified among the 85 Martyrs of England and Wales in 1987.