Is the use of tear gas and chemical laced water justified here

Between 3.30pm to 4.00pm, the 20 thousand crowd , which  had gathered there earlier along Jln Tun Perak were already dispersing.  The following video taken from the 1^st floor of a restaurant shows that the Bersih supporters were leaving Jln Tun Perak and heading away from the direction of Dataran Merdeka, towards Pudu area.  Tear gas gun shots could be heard further down the road towards Masjid Jamek LRT station.

The second part of the video shows the situation at the junction of Jalan Melaka and Jalan Tun Perak.  The Masjid Jamek LRT station is located at this junction and is about 400 metres walking distance away from Dataran Merdeka.

At around 4.15pm, the police had started firing tear gas and chemical laced water at the crowd at this junction.  At around the same time, Chua Jui Ming, PKR Johore chief was telling the crowd at this junction to disperse, saying that Bersih 3 has already achieved its objective.

It was at this time that the police started the spraying of the chemical laced water at the crowd. This was followed a few rounds of chemical water and tear gas fired at about 20 min intervals at this junction, some directly into Jln Tun Perak and some into Jalan Melaka.

The LRT station was closed and there were a few hundred people up there. During this period the train was passing by overhead but did not stop at the station.

This bombardment went on way till about 6pm when the train started picking up passengers again.