He sees him standing there. Therefore he must have come to Verona out of exile.
Paris believes that Romeo has come to Juliet's tomb to cause trouble or desecrate the site, as he is unaware of Romeo and Juliet's relationship and thinks Romeo is a Montague seeking to disrupt the Capulet tomb. This misunderstanding leads to a confrontational encounter between Paris and Romeo at Juliet's tomb.
Paris thinks that Romeo plans to commit some act of desecration or vandalism. Paris is easily prejudiced and is happy to believe that Romeo is an evil monster just because he is a Montague. Compare Paris instantly believing the worst of Romeo to Romeo's compassionate behaviour to Paris.
Paris suspects romeo is attempting to desecrate the tomb.
Paris assumed that Romeo, being a Montague, would want to desecrate the tomb.
At Juliet's tomb, Paris discovers Romeo there and believes he has come to defile the tomb. A fight ensues between them, resulting in Paris being killed by Romeo. Romeo then takes his own life beside Juliet, expressing his love for her even in death.
romeo fights Paris (where?) and Paris dies.
He has come to put flowers on Juliet's grave.
Paris had come to the Capulet tomb to mourn for Juliet. But who should he find there but that nasty banished Montague, Romeo, who is no doubt out to vandalise the Capulet tomb. Paris decides to make a citizen's arrest and to hold Romeo for coming to Verona when he is banished. Romeo asks him to please forget all about arresting him, as Romeo has no intention of harming anyone but himself. But Paris won't listen, so Romeo resists, there is a fight and Paris loses.
To put him next to his love (Juliet). He says, "If thou be merciful, open the tomb, lay me with Juliet". But he only asks this once he has been fatally wounded by Romeo. Romeo had no wish or intent to kill Paris but did after Paris attacked him.
Paris thinks that because Romeo killed Tybalt, he is one of those Montagues that has an insane hatred of Capulets and therefore has come to desecrate the tomb and the bodies within it.
Romeo wins. Paris dies.
Juliet's Parents wanted her to marry Paris not Romeo. Her parents wanted her to marry Paris because Paris and his parents both aren't against Juliet's culture and Romeo was with the other culture. I believe it was there culture but not 100% sure.
Romeo stabs Paris in Act V, Scene III of Shakespeare's play "Romeo and Juliet," when he encounters Paris at Juliet's tomb. Paris believes Romeo is there to desecrate the tomb, and they engage in a heated confrontation, resulting in Romeo fatally stabbing Paris.