Background: Richard I (8 September 1157 - 6 April 1199) was King of England from 1189 until his death. He also ruled as Duke of Normandy, Aquitaine and Gascony, Lord of Cyprus, Count of Poitiers, Anjou, Maine, and Nantes, and was overlord of Brittany at various times during the same period. He was the third of five sons of King Henry II of England and Duchess Eleanor of Aquitaine. He was known as Richard Coeur de Lion or Richard the Lionheart because of his reputation as a great military leader and warrior.
Context: Bad weather forced Richard's ship to put in at Corfu, in the lands of the Byzantine Emperor Isaac II Angelos, who objected to Richard's annexation of Cyprus, formerly Byzantine territory. Disguised as a Knight Templar, Richard sailed from Corfu with four attendants, but his ship was wrecked near Aquileia, forcing Richard and his party into a dangerous land route through central Europe. On his way to the territory of his brother-in-law Henry the Lion, Richard was captured shortly before Christmas 1192 near Vienna by Leopold V, Duke of Austria, who accused Richard of arranging the murder of his cousin Conrad of Montferrat. Moreover, Richard had personally offended Leopold by casting down his standard from the walls of Acre.  Duke Leopold kept him prisoner at Durnstein Castle under the care of Leopold's ministerialis Hadmar of Kuenring. His mishap was soon known to England, but the regents were for some weeks uncertain of his whereabouts. While in prison, Richard wrote Ja nus hons pris or Ja nuls om pres ("No man who is imprisoned"), which is addressed to his half-sister Marie de Champagne. He wrote the song, in French and Occitan versions, to express his feelings of abandonment by his people and his sister. The detention of a crusader was contrary to public law, and on these grounds Pope Celestine III excommunicated Duke Leopold.  On 28 March 1193 Richard was brought to Speyer and handed over to Henry VI, Holy Roman Emperor, who imprisoned him in Trifels Castle. Henry VI was aggrieved by the support the Plantagenets had given to the family of Henry the Lion and by Richard's recognition of Tancred in Sicily. Henry VI needed money to raise an army and assert his rights over southern Italy and continued to hold Richard for ransom. In response Pope Celestine III excommunicated Henry VI, as he had Duke Leopold, for the continued wrongful imprisonment of Richard. Richard famously refused to show deference to the emperor and declared to him, "I am born of a rank which recognises no superior but God". Despite his complaints, the conditions of his captivity were not severe.  The emperor demanded that 150,000 marks (100,000 pounds of silver) be delivered to him before he would release the king, the same amount raised by the Saladin tithe only a few years earlier, and 2-3 times the annual income for the English Crown under Richard. Eleanor of Aquitaine worked to raise the ransom. Both clergy and laymen were taxed for a quarter of the value of their property, the gold and silver treasures of the churches were confiscated, and money was raised from the scutage and the carucage taxes. At the same time, John, Richard's brother, and King Philip of France offered 80,000 marks for the Emperor to hold Richard prisoner until Michaelmas 1194. The emperor turned down the offer. The money to rescue the King was transferred to Germany by the emperor's ambassadors, but "at the king's peril" (had it been lost along the way, Richard would have been held responsible), and finally, on 4 February 1194 Richard was released. Philip sent a message to John: "Look to yourself; the devil is loose".
Question: When was he released?

Answer:
On 28 March 1193 Richard was brought to Speyer and handed over to Henry VI, Holy Roman Emperor, who imprisoned him in Trifels Castle.