Short answers, pulled from the story.
Crusader and Venetian forces besieged and captured Constantinople on the 9th of April 1204 after bad weather initially drove them back. The city was looted, pillaged, and vandalized for three days starting in April 1204 while Emperor Alexios V fled through the Polyandriou Gate.
Boniface of Montferrat and Venetian merchants organized the attack after Alexios IV Angelos promised 200,000 marks of silver and submission of the Eastern Orthodox Church to Rome. Venetians placed Baldwin of Flanders on the throne as Baldwin I of Constantinople because they believed Boniface had too many connections with the former empire.
The total amount looted from Constantinople reached about 900,000 silver marks including 500,000 silver marks stolen by Crusader knights. Venetians received 150,000 silver marks as their due portion according to prearranged treaty terms.
In May 1182 the Massacre of the Latins turned Roman Catholic inhabitants of Constantinople into victims of a brutal uprising led by Andronikos Komnenos. This event shattered political relations between Western Europe and the Byzantine Empire for decades prior to the siege.
Famous bronze horses from the Hippodrome were sent back to adorn the façade of St Mark's Basilica in Venice where they remain there to this day. Works of considerable artistic value were destroyed for their material value including the precious bronze statue of Hercules created by Lysippos which was melted down for minting money.